Stop drafts coming under a door

Adjust the threshold

Raise the threshold until you no longer see light gaps under the door.

Those big screwheads in the threshold
of a newer entry door aren't just
decorative; they raise or lower a
narrow strip set in the threshold.
So if you've noticed a draft under
the door, try this: On a sunny day,
turn off the lights and close nearby
curtains. Lie down and look for
daylight under the door. A sliver of
light sneaking in at both corners of
the door is normal. But if you see
light between the threshold and the
door, grab your screwdriver. Raise
the threshold where light enters by
turning the nearest screws counterclockwise.
Set a straightedge
(such as a framing square) on the
threshold and adjust the other
screws to make sure the adjustable
strip is straight. Close the door and
check for light. Readjust the threshold
until you've eliminated the light.
But don't raise the threshold so high
that it presses too hard against the
weatherstripping on the door.
A too-tight fit will wear out the
weatherstripping quickly.